It is a prior knowledge that a bisphenol compound is produced by allowing a phenol compound to react with a ketone compound in the presence of an acid catalyst. Carried out in most large scale is the production of bisphenol A from phenol and acetone, but corresponding bisphenol compounds can also be produced using phenols having a substituent group on the ring, such as cresol and the like and ketone compounds other than acetone, such as methyl ethyl ketone and the like, as the raw materials.
One of the important use of polycarbonate resins produced using bisphenol compounds as the raw material is for optical use, and products free from coloring and with excellent hue are particularly required for this use. Since bisphenol compounds are melted during the production of polycarbonate resins, in order to comply with these requirements, the bisphenol compounds as raw materials must be excellent in thermal stability so that discoloration does not occur when exposed to high temperature.
As the method for improving thermal stability of bisphenol compounds, a method in which lactic acid, malic acid, glyceric acid or the like is added to a bisphenol compound (Japanese Patent Laid-Open No. 23144/1990), a method in which an aliphatic carboxylic acid or a salt thereof is added thereto (Japanese Patent Laid-Open No. 51338/1993, 51339/1993), a method in which hydroxylamine and a salt thereof is added thereto (Japanese Patent Laid-Open No. 3088/1996) and the like are known. However, the extent of thermal stability improvement effect of bisphenol compound compositions by these methods is still unsatisfactory. Thus, the invention contemplates providing a bisphenol compound composition having excellent thermal stability.